Abstract. We use the stratospheric/tropospheric chemical transport model MOZART-3 to
study the distribution and transport of stratospheric O3 during the
remarkable stratospheric sudden warming event observed in January 2004 in
the northern polar region. A comparison between observations by the MIPAS
instrument on board the ENVISAT spacecraft and model simulations shows that
the evolution of the polar vortex and of planetary waves during the warming
event plays an important role in controlling the spatial distribution of
stratospheric ozone and the downward ozone flux in the lower stratosphere
and upper troposphere (UTLS) region. Compared to the situation during the
winter of 2002–2003, lower ozone concentrations were transported from the
polar region to mid-latitudes, leading to exceptional large areas of low
ozone concentrations outside the polar vortex and "low-ozone pockets" in
the middle stratosphere. The unusually long-lasting stratospheric westward
winds (easterlies) during the 2003–2004 event greatly restricted the upward
propagation of planetary waves, causing the weak transport of ozone-rich air
originated from low latitudes to the middle polar stratosphere (30 km). The
restricted wave activities led to a reduced extratropical downward ozone
flux from the lower stratosphere to the lowermost stratosphere (or from the
"overworld" into the "middleworld"), especially over East Asia.
Consequently, during wintertime (15 December~15 February), the total downward
ozone transport on 100 hPa surface by the descending branches of
Brewer-Dobson circulation over this region was about 10% lower during the
2003–2004 event. Meanwhile, the extratropical total cross-tropopause ozone
flux (CTOF) was also reduced by ~25%. Compared to the cold
1999–2000 winter, the vertical CTOF in high latitudes
(60°~90° N) increased more than 10 times during the two warming winters,
while the vertical CTOF in mid-latitudes (30°~60° N)
decreased by 20~40%. Moreover, during the two warming winters, the
meridional CTOF caused by the isentropic transport associating with the
enhanced wave activity also increased and played an important role in the
total extratropical CTOF budget.